1. Field of the Invention
The present invention relates to a field device, a communication system, and a method for controlling a field device.
Priority is claimed on Japanese Patent Application No. 2013-148666, filed Jul. 17, 2013, the contents of which are incorporated herein by reference.
2. Description of Related Art
In a plant or a factory or the like (hereinafter, collectively referred to as a plant), a distributed control system (DCS), in which on-site devices (measuring instruments, actuators, displays, and alarms) called field devices and control apparatuses to provide control thereof are connected via a communication means, is configured to implement a high level of automated operation. Almost the field devices which constitute such a distributed control system have been performed a cable communication. Recently, field devices for a wireless communication, which meets an industrial wireless communication standard such as ISA100.11a and Wireless HART (registered trademark), are also implemented.
Recently, there have been increased cases that a plant asset management (PAM) system is configured in order to maximize an efficiency of a plant, in addition to the distributed control system described above. The plant asset management system is for operating a plant under optimum efficiency conditions in consideration of information obtained from the field device described above and the like, and operation parameters of the plant and accounting information (raw material expenses, sales price of products, and the like).
Examples of distributed control system of the related art are disclosed in Japanese Patent No. 4399773, PCT International Publication No. WO 2005/050336, and United States Patent Application, Publication No. 2007/0078980. Specifically, these patent publications disclose a distributed control system in which a plurality of field devices and a controller are connected to a network, the controller obtains measurement results from a field device which is a measuring instrument (a flow gauge, a thermometer, and the like), and the controller controls a field device which is an actuator (a valve and the like) based on the measurement results.
Most of the field devices of the related art used in the distributed control systems and the plant asset management systems described above have only the ability to perform basic functions such as a function of transmitting measurement results of, for example, a flow rate or temperature, and a function of adjusting a valve opening and the like under the control of controller (control device). However, recent field devices are digitized and have intelligent functions. Therefore, the number of field devices having additional functions (for example, a self-diagnosis function which is a function of diagnosing one's own condition) in addition to the basic functions described above, have been increasing.
If field devices are digitized and have intelligent functions, in addition to information obtained by the basic functions described above, a variety and large amount of information are obtained from the field devices. For example, information indicating the current state of the field device is obtained from the field device having the self-diagnosis function described above. If such information is obtained, for example, the abnormal of the field device can be promptly detected. Therefore, obtaining such information is thought to be desirable for the safe and efficient operation of a plant. However, if the amount of information obtained from the field device becomes huge, there are cases in which the load of a controller greatly increases.
In the distributed control system described above, all of the measurement results measured by the field devices are collected in the controller, and the controller centrally controls the field devices based on the collected measurement results. Therefore, if a communication failure between the controller and the field device occurs, there are cases in which the controller cannot obtain the measurement results from the field devices and control the field devices. The plant asset management system also operates the plant under optimum efficiency conditions using the information obtained from the field device. Therefore, if a communication failure occurs, there are cases in which the plant asset management system cannot operate the plant under optimum efficiency conditions.